Wifi power saving mode
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{{Midgard article}}
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The tablets support what is called Wifi Power Saving Mode (PSM). PSM allows the tablet to switch its wifi radio on and off several times a second to save battery. While this does greatly improve battery life  (6-8 hours idle on Wifi without PSM, 3-4 days with), there are still many routers on the market which do not support PSM or have a buggy implementation and this can cause problems for the tablets.
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Nokia 770 and n800 supports Wifi Power Saving Mode (often called PSM), in order to improving battery life while keeping network connection.
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== Issues ==
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Unfortunately, a lot of Wifi Access Point (AP) don't support completely PSM and using full PSM mode can cause network trouble.
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Though PSM does greatly increase idle battery life (meaning leaving the tablet connected to a Wifi network at all times is a reality), poor support in some routers and certain network issues can crop up that cause trouble. In the case of routers with non-existent or buggy support, battery life while connected to Wifi may be greatly reduced or, at worst, connection difficulties may arise.
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For Nokia 770 (running with Hacker Edition 2007), it is possible to configure a timeout for enabling PSM (with IT2006, it is not configurable).
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PSM can cause some network issues even on routers with good support. Particularly with PC-to-tablet stuff like [[SSH]], connections may be dropped while idle or lag severely. There are two ways to reduce the negative impact of aggressive PSM in these situations. Either have an active network process running on the tablet (XChat in an active channel, ping to google.com, etc), or [[#Configuration|disable PSM completely]] on connections where you'll be doing a lot of work over SSH.
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To do so, in xterm, run :
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== Configuration ==
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gconftool-2 --set --type int /system/osso/connectivity/IAP/wlan_sleep_timeout 200
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PSM can be configured on a per-connection basis in the Connectivity control panel (Application menu -> Settings  -> Control panel  -> Connectivity). Under the Other tab of Advanced settings when editing a saved connection. There are 3 options available: On (Maximum), On (Intermediate), and Off (note, the WLAN transmission power setting will not significantly impact battery life—though it will impact Wifi roaming distance—and is simply there for legislative reasons). Maximum and Intermediate change the timeout period (200ms and 1000ms, respectively), and Off turns off PSM entirely.
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This will set sleep timeout at 200ms (by default, it is set to 1000ms for IT 2007.3 and earlier. For IT 2007.4 and later, it is set to 200ms).
 
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You might want to try full power saving, by setting timeout to 0.
 
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To reset timeout to default behaviour, run :
 
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gconftool-2 --unset /system/osso/connectivity/IAP/wlan_sleep_timeout
 
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For Nokia n800 / n810, one additional timeout value is available :
 
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inactive_wlan_sleep_timeout (by default, its value is 100ms)
 
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This value is used when lcd display is turned off.
 
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Be sure to test if network latency is still good when testing timeout value.
 
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To test it, with a other device connected on the same subnet, run, after connecting Nokia device to Wifi network :
 
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ping -i 2 192.168.x.y
 
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where 192.168.x.y is IP address of Nokia device.
 
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There is should not be any paquet drop.
 
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You might want to test also with arping -I eth0 -b 192.168.x.y
 
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where eth0 is your interface in the same subnet as Wifi network.
 
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If there is, you should try to increase timeout. Beware using very small timeout (10-100ms) might lead to increase power consumption, because radio chip might be always switching between shutdown and power-on state (when waiting for slow DNS reply for instance).
 
[[Category:Users]]
[[Category:Users]]
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[[Category:Midgard wiki]]
 

Revision as of 02:52, 28 August 2008

The tablets support what is called Wifi Power Saving Mode (PSM). PSM allows the tablet to switch its wifi radio on and off several times a second to save battery. While this does greatly improve battery life (6-8 hours idle on Wifi without PSM, 3-4 days with), there are still many routers on the market which do not support PSM or have a buggy implementation and this can cause problems for the tablets.

Issues

Though PSM does greatly increase idle battery life (meaning leaving the tablet connected to a Wifi network at all times is a reality), poor support in some routers and certain network issues can crop up that cause trouble. In the case of routers with non-existent or buggy support, battery life while connected to Wifi may be greatly reduced or, at worst, connection difficulties may arise.

PSM can cause some network issues even on routers with good support. Particularly with PC-to-tablet stuff like SSH, connections may be dropped while idle or lag severely. There are two ways to reduce the negative impact of aggressive PSM in these situations. Either have an active network process running on the tablet (XChat in an active channel, ping to google.com, etc), or disable PSM completely on connections where you'll be doing a lot of work over SSH.

Configuration

PSM can be configured on a per-connection basis in the Connectivity control panel (Application menu -> Settings -> Control panel -> Connectivity). Under the Other tab of Advanced settings when editing a saved connection. There are 3 options available: On (Maximum), On (Intermediate), and Off (note, the WLAN transmission power setting will not significantly impact battery life—though it will impact Wifi roaming distance—and is simply there for legislative reasons). Maximum and Intermediate change the timeout period (200ms and 1000ms, respectively), and Off turns off PSM entirely.

Retrieved from "http://wiki.maemo.org/Wifi_power_saving_mode"